The present invention relates to hoisting accessories and more specifically refers to a hoisting accessory for cooperation with a hoisting device, for facilitating the placing of a load through openings in walls and the like, said accessory including a support arm having a load coupling unit at one end for carrying the load unit and at its other end a counter weight means which includes a suspension unit fixed to the support arm, and a movable unit which is movable along the suspension unit, said support arm having a lift yoke for connecting said accessory to the hoisting device.
Such accessories are previously known and facilitate, for instance in the erection of buildings, the placing of a load through narrow openings without being obstructed by overhead scaffold ledges or storeys which are a hindrance to the lateral movement of the hoist cable of the hoisting device. U.S. Pat. No. 3,675,961 discloses an accessory of this kind which has an elongate support arm for horizontal suspension when using said accessory. By means of an electric motor a counterweight is displaceable along the horizontal support arm.
However, this and similar prior hoisting accessories are bulky. Moreover, for the displacement of the counterweight some kind of separately energized drive means is required. Said drive means is a source of unreliability as to the function of the accessories and adds to complexity and cost.
An object of the invention is to provide a hoisting accessory for cooperation with a hoisting device, for facilitating the placing of a load through openings in walls and the like, which accessory is simple and moreover does not require any drive means for its operation.
This object is achieved by means of a hoisting accessory to be used in cooperation with a hoisting device for facilitating placing of a load through openings in walls or similar, said accessory having a support arm having at one end a load coupling unit for carrying a load, and at its other end counteweight means which includes a suspension unit connected to the support arm, and a movable unit displaceable along the suspension unit, which movable unit carries the proper counterweight, the support arm having between its ends a lift yoke for connection to said hoisting device. According to the invention said hoisting accessory is characterized in that the suspension unit of said counterweight means from the support arm extends downwards in order to permit, under influence of gravity, displacement of the movable unit along the suspension unit from a retracted position to an extended position, and that a locking device which is releasable in response to loading of the load coupling unit is provided to prevent mutual movement between the suspension unit and the movable unit.
The hoisting accessory according to the invention operates automatically, the movable unit carrying the counterweight being arranged for automatic displacement to the extended position when a load is lifted by the load coupling unit of the support arm, and said movable unit being automatically retractable into the retracted position when said accessory is lowered to rest on a bed, such as the ground.